The present invention relates, in general, to ends for containers. More particularly, the invention relates to openers for such container ends, and in particular to the so-called easy-open type of openers for beverage containers.
Recent advances in the beverage container field have led to the development of all-plastic containers which are commonly referred to as plastic cans, and which have been shown by test marketing to meet with wide consumer acceptance. Although metal cans have long been in use for packaging soft drinks and like carbonated beverages, plastic cans provide a number of advantages.
A "plastic can" may take a variety of shapes, and may be of any desired size, but generally is a cylindrical, wide-mouthed container capable of holding about 12 fluid ounces and is formed of a plastic material such as polypropylene, polycarbonate, polyvinyl chloride (PVC), polyethylene terephthalate (PET), or the like, with PET being the preferred material. Such a plastic has the strength required to withstand the pressures, of up to about 100 psi, which can be generated by a carbonated beverage, limits the permeation, or leakage, of carbon dioxide so that beverages will have a long shelf life, and does not require the internal coating which is needed by metal containers to avoid adverse effects on the taste of the contents. Such a plastic container may be transparent or translucent, and has the consequent marketing advantage of enabling customers to see what they are buying. Further, such a container has good thermal insulating qualities, so that the container does not feel as cold to the touch as does a metal container when the contents are chilled. The body portion of a container of this type is closed at the bottom by a concave, spherical bottom wall to provide the required strength characteristics, and has a wide mouth at the top, preferably extending across substantially the entire diameter of the container, which must be closed after the container is filled.
Initially, such containers were closed with a metal closure of the type referred to as a can "end", which was preferably of aluminum and which was similar to the ends commonly used on metal beverage cans. Such container ends were applied to the upper edge of the plastic body portion by a crimping process after the application of a sealant material between the end and the container. One of the advantages of such a metal end was the ability to utilize a conventional "pop-top" or tear-away opener of the type conventionally used on aluminum beverage cans. However, such ends also had a number of problems. First, the crimping of the ends onto the container involved a multi-step process which was expensive and time consuming. Further, the combination of a metal end with a plastic container was deemed by many to be aesthetically unappealing. Finally, the use of a metal end on a plastic container significantly increased the cost of recycling the container, for the end had to be removed from the can so that the two materials could be separately handled in the recycling process. Since the recycling of materials has become an environmental concern as well as an important factor in the cost of a container, the provision of a container end closure formed of a single material is highly desirable.
The solution to the problem of providing a satisfactory plastic closure for a plastic can was difficult, for it was necessary to devise an end which would be easy to install, which would provide a secure seal, and which would withstand the high pressures generated by carbonated beverages, over a long shelf life. Such an end had to be readily assembled onto the container by automatic machinery and would have to remain in place even during rough handling. In the preferred form, the end would require no sealing material between it and the can, and should provide a closure of the same material as the body of the can.
The solution to the problem of providing a plastic end for a plastic container was solved by the invention disclosed in U.S. application Ser. No. 824,983 of Herbert V. Dutt, filed Jan. 23, 1986, and assigned to the assignee of the present application, the disclosure of which is hereby incorporated herein by reference. As therein described, the top edge of the container is flared outwardly and downwardly to form in cross-section an inverted V shape, with the free end of the curved portion forming a locking flange which extends continuously around the outer periphery of the container. The top edge of the can lies in a horizontal plane which is perpendicular to the vertical axis of the side wall of the container, and the locking flange extends radially outwardly and downwardly at an angle of about 60.degree.-70.degree. from that plane. The plastic closure, or end, is formed from the same material as the body of the container, both of which preferably are formed of PET. The end is shaped to provide a transparent or translucent, dome-shaped concave top wall for the container when the end and can are assembled. The end includes a peripheral, upstanding rim which is curved downwardly and outwardly to define a locking groove adapted to snap over the peripheral top edge of the container side wall and to engage the locking flange. The locking groove is generally in the shape of an inverted V in cross-section to engage to top peripheral edge of the container body. When assembled, the locking groove receives the entire top edge of the container, with the groove and the locking flange of the can cooperating to form an interlocking joint between the two components of the can. The locking flange and the locking groove are so dimensioned as to produce an inward flexing of the container flange as the end is applied, with the flange snapping outwardly over a locking bead formed within the downwardly facing locking groove of the end to hold the end in position.
Although the closure described above provides a simple, snap-on assembly which seals the container and which is capable of withstanding high internal pressures, and which solves the problem of recycling by using the same material for the closure as for the container, nevertheless, one of the major problems in producing an all-plastic can remained; namely, the problem of producing a suitable opener, preferably of the easy-open type. Such an opener must be plastic, again for recycling purposes, must be easy to assemble to the lid for facilitating the manufacturing process, and must provide a reliable seal that will withstand internal pressures of 100-150 psi. In addition, the seal must be non-permeable to gas or liquid, yet must be easily openable by a relatively low pulling or tearing force. No satisfactory easy-open or pull-tab opener has previously been developed for use with plastic can closures, particularly ends made of PET or similar materials of the type disclosed in Ser. No. 824,983.